In this work the effect of aggregation and oxidation on the optical absorption of eumelanin oligomeric sheetsis investigated by applying quantum mechanics and atomistic simulation studies to a simplified eumelaninstructural model that includes 1−3 sheets of hexameric oligomer sheets. The oligomeric hypothesis is supportedby AFM characterizations of synthetic eumelanins, formed by auto-oxidation or electrochemical oxidation ofdihydroxyindole (DHI). Comparison of calculated absorption spectra to experimental spectra demonstrates ared shift in absorption with oxidation and stacking of the eumelanin and validates the theoretical results.